The present invention relates to automatic offset presses in which a series of processes from a printing process through a plate unloading process to a blanket cylinder cleaning process are automatically carried out. More particularly, the invention relates to a plate loading device, a water duct roller mechanism and a form roller mechanism in the automatic offset press.
An offset press is well known in the art in which an automatic plate loading device is provided so that an original plate is conveyed by being held between rollers and is automatically loaded onto a plate cylinder. Then, form rollers are brought into contact with the surface of the plate on a plate cylinder to coat the plate surface with printing ink and a moisture supplying solution, the ink being transferred to the image region.
In the conventional printing machine described above, for an initial period after the plate has been loaded onto the plate cylinder, the plate is not satisfactorily fitted to the plate cylinder using conventional gripper means. Accordingly, portions of the plate, other than those where it is desired to do so, are brought into portions of the plate contact with the form rollers. That is, the ink is undesirably coated onto other than the pattern region.
The portions of the plate surface undesirably coated with ink can be cleaned or the ink stains on the plate surface can be removed while the plate cylinder makes several revolutions. However, since the clearance between the plate cylinder and the rubber blanket cylinder is small, as the plate cylinder is rotated, the ink stains on the portions of the plate which are not satisfactorily fitted to the plate cylinder are brought into contact with the rubber blanket cylinder and transferred onto the cylinder. Accordingly, it is impossible to obtain a satisfactory printing result from the beginning of the printing operation. Therefore, disadvantageously, it is necessary to repeatedly carry out a test printing until a satisfactory printing result is obtained.